298 ADVANCED PHYSIOLOGY 



differently. Cells and fibres are also the main materials of 

 which the cerebellum is made. Figure 152 shows their 

 arrangement diagrammatically. The nerve cells are of 

 several kinds, some showing very complex and some very 

 simple bunches of dendrites. In every case, the cells are 

 located near the surface, while the fibres make up the 

 centre of each lobe. 



The real use of this part of the brain is not thoroughly 

 understood, but there are two main functions which are 

 usually ascribed to it: first, that of a co-ordinating centre. 

 Messages starting from cells in the cerebrum, on their way to 

 the different parts of the body, go to the cerebellum and are 

 there brought together in such a way that the movements 

 which they produce take place in an orderly, related manner. 



In every human being several activities are going on at the 

 same time. In ordinary walking, for example, the muscles in 

 one leg are contracting while corresponding muscles of the other 

 are relaxing. While a person is walking it is entirely possible 

 for the muscles of the neck to turn the head, for those of the 

 tongue and mouth to be concerned in speaking, and for those 

 of one hand to be contracted about a package or umbrella. 

 Thus, although one does not frequently think about it, all our 

 habitual activities involve a very complicated nervous mech- 

 anism. This direction of movements so that many muscles 

 may work together toward a single end is called co-ordina- 

 tion, and is one of the functions of the cerebellum. Impulses 

 provoking movements start in the cerebrum, but are regulated 

 in the cerebellum. An animal from which the cerebellum has 

 been removed is unable to control or direct the movements 

 of the various body muscles and cannot perform even the 

 slightest action in an orderly, straightforward manner. 



A second function of the cerebellum which has been em- 

 phasized by some physiologists is that of a relay station for 

 outgoing impulses from the cerebrum, strengthening the force 

 of nerve messages on their way to the lower muscles of the 







